1. Field
Embodiments of the present invention relate to a wireless communication system, and more particularly, to a technology for allocating a Channel State Information-Reference Signal (CSI-RS) in a wireless communication system.
2. Discussion of the Background
With the development of communication systems, a wide variety of wireless terminals are being used by consumers, such as business companies and individuals.
Mobile communication systems, such as 3GPP (3rd Generation Partnership Project) including LTE (Long Term Evolution) and LTE-A (LTE Advanced), allow for the development of technology for a high-speed large-capacity communication system, which can transmit or receive various data, such as images and wireless data, beyond the capability of providing a voice service, and can transmit data of such a large capacity as that transmitted in a wired communication network. Moreover, the current mobile communication systems are requiring a proper error detection scheme, which has a goal to minimize the reduction of information loss and improve the system transmission efficiency, thereby improving the system performance.
Further, in various current communication systems, various Reference Signals (RSs) are used in order to provide information of a communication environment, etc. to a counterpart device through an uplink or a downlink.
For example, in a Long Term Evolution (LTE) system, which is an evolved system for mobile communication, a Cell-specific Reference Signal (CRS) is transmitted as a reference signal at each sub-frame in order to obtain channel information in the downlink transmission.
At this time, since the maximum number of antennas supportable in the downlink of the LTE system is four, different CRSs are allocated to and transmitted through a maximum of four antenna ports according to the time/frequency.
The next generation communication technologies, such as the LTE-A, can support eight antennas in the downlink. Therefore, the current CRSs defined for four existing antennas are insufficient for detection of channel information at the time of downlink transmission. In order to overcome such a problem, a reference signal named “Channel State Information-Reference Signal (CSI-RS)” has been newly defined to obtain channel state information of a maximum of eight antennas.
In other words, a communication system using a maximum of eight Multiple Input Multiple Output (MIMO) antennas at both the transmission port and the reception port may be used, and a scheme of transmitting CSI-RSs, UEs of which are different according to the antenna ports or antenna layers for the transmission or reception of the signals, may also be used. Presently, only basic definitions for the CSI-RS and definitions for the resource overhead have been arranged. However, methods for allocating corresponding CSI-RS patterns to resource areas by each antenna port in each eNB (or eNodeB) or cell have not been specifically arranged yet.
Especially, the length of the Cyclic Prefix (CP), Duplex scheme, etc. may change the form or type of the subframe to which the CSI-RSs will be allocated. However, there has been no discussion about a scheme for allocating CSI-RSs to each antenna port in such a case.